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Just for reference, with a wooden, fixed pitch prop, I could get no
more than about 2350 RPM for a sealevel takeoff and takeoff was a bit
on the anemic side, to say the least. With the CS unit, I always get
2650-2700 RPM and the takeoffs are now quite sprightly affairs.
     
Do the numbers; that's better than a 10% increase in takeoff horsepower
(HP = T x RPM / K [K is a constant around 5200 for these regimes]).
Nearly all of it is "excess power" needed to climb, which relates to
better takeoff performance.
     
Cheers,
     
Dan Schaefer
<<<<
          
     An addition to Dan Schaefer's response to Sven (SE-XOP) regarding
     props.
     
     The constant mentioned in the HP = T x rpm / k is fallout from the unit
     conversions required:
     hp = 550 ftlb/s
     T = ftlb
     rpm = (2*pi rad/s)/(60s/min)
     
     put it all together and you get:
     
     HP [550 ftlb/s] = T [ftlb] x rpm [(2*pi rad/s)/(60s/min)]
     HP = T x rpm /(550 ftlb/s x (60s/min)/(2*pi rad/s))
     HP = T x rpm / 5252
     
     With a CS prop, in addition to the engine putting out more horse power
     at the higher take off rpm, more of the prop blade is flying and
     providing thrust.  A fixed pitch cruise prop can have a substantial
     portion of the blade in a stalled condition until sufficient forward
     velocity is obtained.  If the pitch is too steep, enough of the blade
     can be stalled such that the aircraft can't accelerate at all.  In
     this case all of the horse power being generated is going into
     stirring a lot of air and providing no thrust.
     
     Dan, your % thrust increase was probably much higher than your % power
     increase.
     
     CS all the way.
     
     Chris Zavatson
     N91CZ